1. Field of the Invention
The present invention relates generally to object sensors and related methods, and in particular relates to electronic object sensors and methods useful in detecting vehicle speed and shape for classification and input to Intelligent Vehicle Highway Systems (IVHS).
2. Background Art
A vehicle sensor providing the presence of a vehicle in a traffic lane and indicating the vehicle speed as it passed the sensor is disclosed in copending Application Ser. No. 07/980,273 referenced above. A time-of-flight laser rangefinder concept is used which measures the normal distance to a highway from a fixed point above the road surface and then measures the distance to any vehicle which either passes or stops under the sensor. The concept teaches the use of two laser beams pulsing at a high rate projected across the road surface at a fixed angle between them. Because of the high repetition rate, the system is also able to determine vehicle speed with an accuracy within one mph and using this calculated speed, develop a longitudinal profile of the vehicle using consecutive range measurements as the vehicle moves under the sensor.
The principal goals of the invention are to provide active near-field object sensors which are relatively low in cost, are accurate and have utility in a wide variety of applications. The invention contemplated a sensor for detecting the presence of an object within an area located in a close range to the sensor, and includes a range finder having means for emitting a directional output of pulsed energy toward the fixed area. In a preferred arrangement, the emitting means comprises a laser diode capable of emitting pulses of coherent infrared radiation, which are used together with collimating optics and a beam splitter to provide two diverging output beams directed toward the near-field area under observation.
The sensor also includes means for receiving a portion of the energy reflected from either the area, or an object located within the area. The returned pulse energy is then provided as an input to a receiver for determining a time of flight change for pulses between the emitting and receiving means, which may be caused by the presence of an object within the area. The sensor is also provided with various features useful in providing outputs which indicate either the speed, census, size or shape of one or more objects in the area. For example, the sensor is provided with means for receiving an input from the time of flight determining means and for providing an output indicating whether the object meets one of a plurality of classification criteria (e.g., is the object an automobile, truck or motorcycle). To achieve these and other objectives, the receiving means includes two detectors, with means for alternately selecting between the outputs of the two detectors for providing inputs to the time of flight determining means; means are also provided for measuring the time interval between interceptions of the two diverging outputs by a given object, so as to calculate the speed of the object passing through the area.
Copending application Ser. No. 07/997,737 referenced above discloses the generation of three dimensional images of objects by rotating or scanning a laser beam rangefinder, operating at a high pulse rate, in a plane where there is relative motion between the rangefinder and the object to be sensed or imaged in a direction perpendicular to the laser beam plane of rotation. This operation causes the laser rangefinder rotating beam, when passing to a side of the object, to cover the object to be sensed with rangefinder pulses, and thereby, obtain a three dimensional image of the object.
A preferred embodiment of the three dimensional object sensor taught in the copending application taught the sensing of trees formed in a row for purposes of spraying, counting or measuring the size of the trees. The sensor is moved along the ground traveling between rows of trees, crops or foliage with the laser rangefinder scanning on either side of the moving vehicle carrying the sensor in a plane perpendicular to the motion of the vehicle. When the sensor detects the presence of foliage, it provides a signal activating a spraying system for the efficient spraying of the tree or object being sensed. This operation ensures that spraying takes place only when there is foliage present to intercept the sprayed materials. Economic and environmental benefit is thus realized.
The agricultural sprayer employs a pulsed time-of-flight range measuring system having separate apertures for the laser transmitter and receiver. The laser beam and receiver field-of-view are continuously scanned, by a rotating mirror, in a vertical plane which is perpendicular to the forward motion axis of the sprayer vehicle. The position of the mirror, and correspondingly the laser beam, is determined by means of a shaft encoder attached to the mirror drive motor shaft. With this embodiment, a single sensor makes range measurements on both sides of the sprayer vehicle as the vehicle moves the sensor between rows of trees. Since the sensor only need to detect the presence of trees, range measurements are only made within elevation angles of plus and minus 45 degrees on each side of the sensor. Data is collected within 180 degrees out of the 360 degrees of a revolution or circular scan. As the sprayer vehicle moves along, the scan trace advances on consecutive revolutions of the mirror. Employing a distance traveled input from the vehicle, the sensor creates a panorama of images. An algorithm then determines whether trees are present from the measured range data as a function angle. Spray units are grouped in zones and the sensor provides foliage images for the zones and thus an indication of the amount of spray necessary for a particular tree zone.
There is a continuing demand for accurate, low-cost sensors useful in a wide variety of applications, including equipment used in the home, as well as for security, military and transportation applications. There have been suggestions for traffic signal controllers utilizing overhead sensors. Copending application makes reference to the following U.S. Pat. Nos. 3,167,739 to Girard et al; 3,436,540 to Lamorlett; 3,516,056 to Matthews; 3,532,886 to Kruger et al; 3,680,047 to Perlman; and 4,317,117 to Chasek.
Likewise referenced, near-field sensors have also been utilized as intruder alarms and as automatic door operators. Examples of such arrangements are disclosed in the following U.S. Pat. Nos. 3,605,082 to Matthews; 3,644;917 to Perlman; 3,719,938 to Perlman; 3,852,592 to Scoville et al; 3,972,021 to Leitz et al; and 4,433,328 to Saphir et al.
As discussed in the three dimensional sensor copending application, U.S. Pat. No. 4,768,713 discloses the use of an ultrasonic sonar-type sensor to detect the presence of tree foliage, as do U.S. Pat. No. 4,823,268 and U.S. Pat. No. 5,172,861. Optical dimensioning techniques have been incorporated in industrial uses as disclosed in U.S. Pat. No. 4,179,216 and U.S. Pat. No. 4,490,038.
As discussed in the copending applications, the object sensors were developed by the inventors as an outgrowth of several laser systems developed for Department of Defense and Department of Transportation programs. Typically military use of laser optics and electronics are found in missile systems and target recognition systems. Target images are produced and are seen as a missile or carrier flies over a targeting area. For example, a missile may be equipped with a laser range finder scanning in a plane perpendicular to the flight path.